Cell transplantation into immune compromised mice has transformed our understanding of human disease and has been used extensively to assess regeneration, stem cell self-renewal, and cancer. Despite the great utility of xenograft cell transplantation into immune compromised mice, mouse models are not amenable to large-scale studies due to high husbandry cost and do not facilitate direct visualization of engrafted cells. B contrast, zebrafish are inexpensive, can be reared in large numbers, and are amenable to large-scale chemical genetic approaches where compounds can be added directly to the water. Optically clear caspar-strain zebrafish lack pigmentation, facilitating the direct visualization of fluorescent cells in live adult animals. Moreover, cell transplantation utilizing genetically-identical, syngeneic zebrafish strains has validated that large-scale cell transplantation using hundreds of recipient animals is possible. Finally, zebrafish can be raised at 35C and thus a potential model for engraftment of human and mouse cells. Despite these clear advantages of the zebrafish model, the use of immune compromised zebrafish for xenograft cell transplantation has yet to be reported. Capitalizing on optically-clear caspar-strain zebrafish and recently developed gene inactivation using TALENs, we will develop zebrafish lines with similar mutations found in immune compromised mice that are commonly employed for xenograft cell transplantation. Aim 1 will develop zebrafish lines that are deficient in forkhead box N l (foxnl/nude), recombination-activating gene 2 (rag2), Janus kinase 3 (jak3), DNA-dependent protein kinase (prkdc), and interieukin 2-receptor gamma (IL2rg). Aim 2 will assess each model for the ability to engraft fluorescent-labeled normal and malignant cells from zebrafish, mouse, and human. Transplant engraftment will be assessed in single mutant fish and compound mutants for 1) rag2-/-, jak3-/-; 2) rag2-/-, 112rga-/-, 112rgb-/-; 3) prkdc-/-, jak3-/-; and 4) prkc-/-, IL2rga-/-, Il2rgb-/-. These experiments will allow comprehensive comparison of engraftment between zebrafish mutant lines. Aim 3 will establish an organizational structure to rapidly and efficiently distribute viable mutant lines to the research community. The experiments outlined here will develop a much-needed resource for the community, facilitating the next generation of low-cost, high throughput cell transplantation models. Such broad reaching applications for immune compromised zebrafish spans the mission of many NIH institutes.